The present disclosure relates to a piezoelectric device such as an angular velocity sensor, a piezoelectric actuator, and a pyroelectric infrared ray sensor, a production method thereof, and an electronic apparatus equipped with the piezoelectric device.
In the past, lead zirconium titanate (hereinafter, referred to as PZT) is used for a piezoelectric film used in a piezoelectric device such as an angular velocity sensor. Various techniques are proposed for improving piezoelectric characteristics, ferroelectric characteristics, pyroelectric characteristics, and the like of the PZT.
Japanese Patent Application Laid-open No. Hei 06-350154 (hereinafter, referred to as Patent Document 1) discloses a PZT thin film whose crystalline structure is rhombohedral, in which, when lead zirconium titanate is represented by Pb1−Y(ZrXTi1−X)O3+Y, a PbO excessive composition ratio Y is within a range of 0≦Y≦0.5, and a Zr composition ratio X is within a range of 0≦X≦0.55.
Japanese Patent Application Laid-open No. 2005-5689 (hereinafter, referred to as Patent Document 2) discloses a piezoelectric element constituted of a first electrode film, a second electrode film, and a piezoelectric thin film sandwiched between the first electrode film and the second electrode film. The piezoelectric thin film is constituted of an oxide piezoelectric thin film having an oxygen loss larger than 0% and equal to or smaller than 10% with respect to a stoichiometric composition. Moreover, the piezoelectric element equipped with a piezoelectric thin film having such an oxygen loss has stronger piezoelectric characteristics than an oxide piezoelectric thin film having a stoichiometric composition. 
Japanese Patent Application Laid-open No. 2007-116091 (hereinafter, referred to as Patent Document 3) discloses a piezoelectric body including a first ferroelectric substance crystal that has a crystal orientation when not applied with an electric field, the piezoelectric body being provided with characteristics with which, due to an application of an electric field of a predetermined electric field intensity or more, at least a part of the first ferroelectric substance crystal undergoes a phase transition to a second ferroelectric substance crystal having a different crystal system from the first ferroelectric substance crystal. According to this piezoelectric body, a large distortion displacement amount can stably be obtained.
Incidentally, when heated, a piezoelectric material is known to deteriorate in piezoelectric performance, which is called depolarization. However, because a heat treatment by solder reflow and the like is generally carried out in a process of mounting electronic components on a wiring substrate, there is a problem that the piezoelectric performance of the piezoelectric material deteriorates due to the heat.
Particularly in recent years, a solder reflow temperature is increasing due to lead-free soldering in consideration of environmental problems, and heat caused by the solder reflow causes the piezoelectric performance of the piezoelectric material to deteriorate, which is problematic. However, Patent Documents 1 to 3 above give no consideration to the effect of heat.
In view of the circumstances as described above, there is a need for a piezoelectric device having excellent heat resistance, an angular velocity sensor, an electronic apparatus, and a production method of a piezoelectric device.